Method of and means for reducing retroactive currents in push-pull amplifiers



Nov. 3, 1925- 1,560,332

s. BALLANTINE METHOD OF AND MEANS FOR REDUCING RETROACTIVE CURRENTS IN PUSH-PULL AMPLIFIERS Original Filed April 1923 Patented .Nov. 3, .1925 I I UNITED" STATES [PATENT OFFICE.

STUART EALLANTINE, or WHITE H VEN, PENNSYLVANIA, AssIeNoR TO RADIo FRE- QUENCY LAEoRA'roRIEs, INCORPORATED, or BOON'ION, NEW JERSEY, A CORPORA- TIQN E N EW JERSEY.

METHOD or AND MEANS FOR REDUCING RErRoAcTIvE cUnRENTs IN PUSH-PULL AMPLIFIERS.

Original application filed April 3, 1823, Serial No. 629,702.. Divided and this app'li caton filed July 3,

To all whom it may concern.

it lrnown that l, STUART BALLANTINE,

I a citizen ot'the United States, residing at ill active orieed-back current due to the gridplate impedance of the audion amplifying! tubes."

This application is a division of my copending application, Ser. No. 629,702, filed April 3, 1923, which relates to the reduction or elimination of retroactive currents in three-electrode ionic amplifiers, which ourrent-s arise from-the capacity coupling between the input and output circuits of the amplifier.

' In my'copending application I have described the method of and circuits for balancing the impedance network of a one tube amplifying stage to reduce or eliminate retroactive currents through the grid-plate impedance. In the present case, the output til) circuit of one ionic amplifying tube is so balanced, according to themethods de scribed in my earlier application, against the output circuit of a similar tube that there is no retroaction from either output circuit upon a common input circuit.

in the accompanying drawings whichillustrate embodiments of my invention, I

Fig. 1 is a symbolic representation of a I push-pull amplifying unit comprising two ionic amplifiers; I 1 V Fig. 2 is a diagrammatic representation of various forms of impedances which may.

be em loyed as the input impedance network or the unit shown in Fig. 1; and

Fig. 3 'is adiagram of a balanced pusl1- vpull amplifying circuit. I

In Figure 1, T and T are ionic amplifiers having a common filament battery A and a common plate battery B. C andC are intra-electrode capacities oii'T and T reback through C and C 1924. Serial No. 724,123.

spectively, which produce undesirable reactive effects when unbalanced; Z anc' Z are neutralizing impedances which eliminatethis retroactive effect. Z and Z are respectively the input and output coupling networks which satisfy the following requirements:

- (1) In Z the potential difference. be tween Sand 4 due to an input voltage im pressed between and 2 must be' opposite in phase with respect to the common point l to the voltage acting between 4 and 5.

(2) In Z the potential dilierenee be tween 6 and 7 resulting from a flow of A. C. plate currents must be opposite in phase, with reference to point 7, to thevoltage act ing between 7 and 8.

(3) In 5d,, the impedances between (i and 7 and between 7 and 8 must include a D. C, path for the direct components of plate current of tubes T and T since these impedances are in series connection with the plate I circuits.

Various forms of connectingnetwork suitable for use at Z, and Z are shown in Fig. 2. Separation of the input and output circuit occurs when there is no component of voltage between 3 and 4 and between at and 5 due to retroactive currents flowing To show how this'balance may be'ohtain'ed in a particular circuit, the embodiment of my invention shown diagrammati cally in Fig. 3 is presented, Here the input network corresponding to Z takes the form of a transformer having a primary winding or windings '1--2, and two secondary wind-- ings 3-4 and 4-5, While Z is a similar transformer having two primary windings L and L provlding the impedances correspending to 6-7 and 7*8, respectively, of

Fig. 1, and secondary windings L and Ii,

corresponding to the impedance- 9-10 of Fig. 1. For the purpose of makin the transformer windings resonant'to di erent. frequencies, tuning condensers C C, and

68, 9--10 and 3-5-5, respectively, or if. desired, variable transformers may be used in C, may be shunted across the impedances'.

addition or in lieu ofthe tuning condensers.

The neutralizing impedances in this arrangement take the form of condensers C and C which are. located, respectively, between points 5 and 6 and between points 3 and 8 of the impedance networks. If the tuning to various frequencies is done by means of the variable condensers, G C C the neutralizing condensers C C need no readjustment for changing frequencies. If the tuning is done by means of variable transformers, or variable inductances in conjunction with or in lieu of condensers, the combinations L L and. L L, should be varied together for independence of frequency. I have found that this can readily be accomplished by using variotransformers, such as described in my copending applications Serial No. 590,514, filed September 25, 1922, and Serial No. 607,852,.liled December. 19, 1922, and in the .copending application of L. M. Hull, Serial No.

611,118, filed January 6, 1923, when these variotransformers are mechanically connected so that they may be rotated together.

It can be shown by analysis of the circuits that the opposition in phase of the input voltages upon the tubes produces such a phase relation between the output currents that the potentials of G, and G are unaffected by currents through C and G The load introduced through the windings of Z is so balanced with respect to C and C, that the current flowing through. L and C to G is just neutralized by the current flowing through L and C to G with .a similar relation holding for the currents to G through 0 and L O and L This balance can be attained with a variety of different circuit constants, as will be apparent to one skilled in the art. For example, if the ionic tubes T and T have exactly similar characteristics and the load is equally balanced upon the two tubes by making L,=L,, and L :L,, then 0 must.

be made equal to C and both bear a ratio to C and O which depends upon the absolute values of L and L and the constants of the tubes and which can be readily found by experiment in any given case.

\Vhile I have described the'perfect balancing of the impedance network to secure a complete elimination of the retroactive effect, it will be understood that my invention it not restricted to a perfect balance, since any tendency towards balance with reduce tion of the retroaction, or control of it, falls within the scope of my invention. It will also be understood that'the invention is not limited to the specific circuit which I have described, since various changes ormodifications may be; made in the circuits without departing from the spirit of my invention. i

I claim 1. The method of preventing the output circuits of a push-pull amplifying stage from affecting the input circuit of said stage, which comprises balancing the retroactive current due to the output circuit of one tube of said stage by a neutralizing current established by the output circuit of the other tube of said stage.

:2. The method of preventing the output circuit of an audion push-pull amplifier network from affecting the input circuit terminals which comprises neutralizing the effect of a retroactive current through the gridplat-e impedance of one audion by impressing a second retroactive voltage upon the grid of that audion, said second retroactive voltage being established by the load in the plate circuit of the secon audion.

3. An amplifying stage comprising input and output circuits, two audions oppositely connected in said circuits whereby one of said audions isadapted to repeat certain parts, and the other, the remaining parts ofincoming waves, and a coupling between said-input and output circuits for each of said audions and effective to counteract the effect of retroactive currents through the grid-plate impedance, of its respective audion.

4:. An amplifying stage comprising input STUABT BALLANTINE.

' ture. 

